The reinfection pattern of Metagonimus yokogawai was studied at Tamjin river
basin, one of its well-known endemic areas in Korea. Stool specimens of a total of 230
inhabitants were examined and 68 (with high egg counts) out of 99 positive cases were
treated with 10 mg/kg single dose of praziquantel in January 1984. Follow-up stool examinations
were performed every 3 months for a period of one year.
The results were as follows:
1. The pretreatment egg positive rate was 43.0% and their average EPG 1,560 (range; 020,800).
The rate in male inhabitants was higher (46.9%) than in females (39.3%), and age
groups older than 21 (male) and 31 (female) years revealed over 70% and 60% positive rates,
respectively.
2. After the treatment, the rate in whole subjected people decreased to 16.7% in April, but
increased thereafter to 24.5% in July, 24.7% in October and 32.1% in January ('85). The
average EPGs in April and July were remarkably lower than before treatment, but it returned
back to or exceeded the pretreatment level in October and January('85).
3. Up to half (10.6-54.3%) of the treated inhabitants appeared reinfected during the
follow-up period, while only a few proportion (3.4-7.9%) of uninfected cases turned to egg
positive. Approximately a half of infected but untreated cases turned to egg negative, which
suggests spontaneous cure.
From the results, it is inferred that new infection by M. yokogawai occurs mainly in the
season from mid-summer (July) to late autumn (November or so), especially to people who
like to eat raw sweetfish.